This invention relates to transducers or loudspeakers which are driven by a rotary drive means rather than by a conventional voice coil.
As described in U.S. Pat. No. 4,564,727, incorporated herein by reference, a greatly superior subwoofer having a very high power handling capacity is made possible by using a commutated servomotor as the drive, rather than a conventional voice coil. In such a device, the motor shaft is connected by a linkage to one or more diaphragms. The use of a commutated rotary motor allows for unlimited excursions of the diaphragm at high power levels. In order to accomplish this result, it is necessary to use a suitable device to convert rotary motion of the motor into linear motion at the diaphragm. The diaphragm may take the form of a panel or of a heavy duty speaker cone.
In producing sound of high intensity, especially at low frequencies, there are several limiting factors in conventional systems. Conventional speakers for many years have used electromagnetic voice coils, which have numerous inherent limitations. Some of these limitations include limited excursion due to limited coil length and resistance, limited heat capacity, and limited magnet size. Also, the most modern speaker cones have a limited excursion of a maximum of about one-half inch. Since available acoustic source strength is dependent on the displacement or surface area of the radiator or diaphragm, the prior art has proposed the use of larger speakers in large enclosures. In order to drive the speaker, larger and heavier voice coils must be employed, which result in severe resistive heat losses and possible thermal degradation of the voice coil.
While the servo-drive loudspeaker of U.S. Pat. No. 4,564,727 overcomes or avoids most of the aforesaid problems, it would be desirable to provide further improvements to simplify the system and provide a low frequency transducer with fewer moving parts and smaller overall size.